The present invention relates to a method, apparatus, and test kit for measuring and monitoring the concentration of a cleaning agent in a liquid, more particularly a surfactant-based neutral cleaning agent in a wash liquor.
In commercial cleaning of process oils and grease from metal parts, tools and other metal surfaces commonly found in maintenance departments, auto service shops, and metal processing industries, there has been a shift over the years from solvent washer systems to aqueous-based cleaners. Of those cleaners, alkaline cleaning products have become widely used.
Alkaline cleaners chemically react with most oils by saponification, whereby the oil is chemically changed to a partially soluble soap, which cannot be easily separated from the wash water. A drawback of alkaline cleaning products is that they cannot be discharged to a sewer system due to heavy metals and chelators in the solution. In addition, the high alkaline pH between 8.0 and 12.0 further complicates the wastewater treatment process. Alkalines also become consumed during the saponification process, which necessitates constantly adding more cleaner to replace what has been consumed.
The advent of surfactant-based neutral cleaners (SBNs) has provided a new option for aqueous degreasers for cleaning hard surfaces. SBNs have a neutral use pH of between 7.0 and 8.0, and are all organic, provide superior rinsability, greater foam control, mildness to the skin, longer shelf life, eliminate many wastewater problems and washer corrosion, do not leave the characteristic white film of alkaline products, and provide an xe2x80x9call-in-onexe2x80x9d product that is safe on all kinds of metal surfaces. In the area of wastewater treatment, SBNs reduce the need for pH adjustment prior to discharge, thus eliminating the costs associated with acid neutralization. Because of the neutral pH, bioremediation becomes a viable wastewater treatment option. Unlike alkaline degreasers, neutral cleaners clean by a mechanism of emulsification whereby they surround oil molecules with a micelle formed by agitation and impingement of the oily surface. The micelles prevent the oil from re-attaching to the metal surface and, when the agitation stops, release the oil to the surface where it can be removed by traditional recovery methods. Unlike alkalines, once the excess oil is recovered, the neutral soap is available for cleaning again, which extends the life of the bath solution.
In a wash process, it is desirable to monitor the concentration of the cleanser in the wash solution throughout the operation in order to maintain the cleanser at a consistent level. Current methods for testing the concentration of an alkaline detergent in a wash liquor include fluorescence, conductivity and, most commonly for metal cleaners, acid-base titration based on a phenolphthalein indicator end point. A drawback, of these methods is that they give an inaccurate analysis due to soil loading. In addition, conductivity must be empirically determined for each detergent.
U.S. Pat. No. 5,4998,546 (Kuhlmann et al.) discloses another method for determining the concentration of an alkaline detergent in an industrial laundry wash liquor, by adding a reducing sugar to the wash liquor in an amount proportional to the detergent composition, chemically reacting the sugar with an aromatic hydrazine compound, and photometrically measuring the color. However, the test procedure is time consuming, and requires multiple reagent solutions, heating and temperature control for accurate results, and an extended reaction time to induce a color change. In addition, a PC is needed as an instrument-operator interface, relatively complicated instrumentation is used, the set-up is expensive, and frequent-calibration of instruments is required.
Currently used methods for determining the concentration of SBNs in a washer bath are acid-base titration and EDTA titration, which involve adding an indicator to a small volume of the wash solution and measuring the amount of titrant required to induce a color change. Problems with these methods include interference caused by lubricants, oils, rust inhibitors and additives in the washer bath, inconsistent results from bath to bath, the need for multiple chemical reagents, difficulty in distinguishing a color change in a dirty or murky bath, and the need to conduct multiple steps for the analysis. In addition, the use of EDTA in the cleaner formulation as a metal chelator causes wastewater concerns due to increased heavy metal discharge. To date, there are no procedures for readily and accurately testing the concentration of a surfactant-based neutral cleaner (SBN) in a wash liquor.
Therefore, an object of the invention is to provide a method for readily and accurately determining the concentration of surfactant-based neutral cleaners (SBNs) in a wash liquor that overcomes the disadvantages of current testing methods.
These and other objects are achieved by the present invention, which is directed to a method of determining the concentration of a cleaning agent in a wash liquor, particularly a surfactant-based neutral cleaning agent, an apparatus for carrying out the method, and a test kit containing the apparatus and associated test items and reagents.
According to the method, a wash liquor is combined with a solution containing a mixture of the cleaning agent, an amount of a reducing sugar that is proportional to the cleaning agent, and a sugar preserving agent. The solution of the cleaning agent and reducing sugar preferably contains about 0.5-3.0% reducing sugar, more preferably about 2%. To test for the concentration of the cleaning agent in the wash liquor, an aliquot or portion of the wash liquor is removed and reacted with an enzyme composition to induce an enzymatic reaction with the reducing sugar and produce a colored reaction product. The enzyme composition is typically composed of an oxidase enzyme, peroxidase, and an indicating agent that will produce a colored product when the sugar is reacted with the enzyme composition. In the use of glucose as the reducing sugar, glucose oxidase is a preferred component of the enzyme composition.
The intensity of the color of the enzyme/sugar reaction product can be measured photometrically using light at an appropriate wavelength. The color intensity value is then correlated with the concentration of the reducing sugar, which, in turn, is correlated to the concentration of the cleaning agent in the wash liquor. An approximate concentration of the reducing sugar in the wash liquor can be determined by comparing the color of the reaction product to a color chart.
The method is useful for monitoring the concentration of the cleaning agent in a wash liquor over time by occasionally or at set intervals, removing a portion of the wash liquor, reacting it with the enzyme composition, and measuring and correlating the color intensity of the reaction product to the concentration of the cleaning agent in the wash liquor.
In a preferred method, an aliquot of the wash liquor is deposited onto an enzyme composition that is immobilized on a solid support such as a plastic test strip. The intensity of the color of the reaction product can be determined photometrically by transmitting a beam of light at the desired wavelength onto the solid support and to a light detector that receives the light reflected from the reaction product.
In implementing the method, it is desirable to use a portable, hand-held apparatus that is designed to measure the concentration of the reducing sugar and correlate that amount to the concentration of the cleaning agent in the wash liquor. Such a device includes a member for removably receiving the solid support (test strip), a light source for applying a beam of light at the desired wavelength onto the solid support, and a member for detecting the light reflected from the reaction product on the solid support. The detecting member is operable to produce an output signal that is proportional to the light that is detected. The device further includes a microprocessor that receives and processes the output signal, and is programmed to correlate the output signal to the concentration of the reducing sugar and, preferably, to process and correlate the concentration of the reducing sugar to the concentration of the cleaning agent in the wash liquor. In use of the apparatus, a test strip with the enzyme composition immobilized on it is inserted into the receiving slot, and a drop of the wash liquor is deposited onto the enzyme composition. The enzymatic reaction typically proceeds for about 30-60 seconds, whereupon the apparatus photometrically measures the color intensity of the reaction product and processes the data to arrive at the concentration of the reducing sugar, and preferably the cleaning agent, in the wash liquor. The value is then displayed and/or printed out for the user.
A test kit is provided that contains the portable, hand-held apparatus packaged together with other items and reagents used in the test method. Such items can include test strips with the enzyme system immobilized thereon, instructions for using the apparatus and other testing items according to the method of the invention, a calibration standard curve of the sugar concentration versus the cleaning agent concentration, and optionally, a container or package of the cleaning agent, reducing sugar and sugar preservative.
Advantageously, the present method provides a quick, easy, accurate, and reliable assay for testing the concentration of a surfactant-based neutral cleaner in a wash liquor. The assay employs an indicating agent, i.e., the reducing sugar, which is biodegradable and non-toxic, eliminates the need for hazardous chemical reagents, and will not affect the wash process or cleanliness of the part or item being cleaned. The present method and apparatus also decrease the time required for testing the amount of cleaner in a wash liquor, and requires the use of relatively inexpensive instrumentation.